Many utility lines, pipelines and other underground components are installed in or under the ground by boring a borehole in a generally-horizontal direction in the ground rather than by digging a trench. This type of construction, which is sometimes referred to as “horizontal boring”, “directional drilling” or “horizontal directional drilling”, eliminates the need to excavate earth in order to install an underground component, and thereby saves several steps in the installation process. If no trench is dug, there will be no trench to fill, and no disturbed surface to reclaim. The horizontal drilling machine may be operated to drill a pilot bore along a planned path underground. Typically, the planned path is generally arcuate in shape from the entry point at the surface of the ground, continuing underneath a roadway, river or other obstacle, to the exit point at the surface on the other side of the obstacle.
A typical directional drilling machine includes a thrust frame that can be aligned at an oblique angle with respect to the ground. Mounted on a drive carriage on the thrust frame is a pipe-rotation mechanism that is adapted to rotate a series of interconnected pipe sections (commonly referred to as a drill string) about a boring axis. The drive carriage also includes a carriage drive assembly that is adapted to push the carriage along the thrust frame. The combination of rotation of the drill string and longitudinal movement of the drive carriage along the thrust frame causes the drill string to be advanced into or withdrawn from the ground.
To drill a hole using a directional drilling machine, the thrust frame is oriented at an oblique angle relative to the ground, and the drive carriage is retracted to an upper end of the frame. A pipe section is unloaded from a magazine and is coupled to the pipe-rotation mechanism on the drive carriage. A boring tool or cutting head is mounted to the distal end of the pipe, and the drive carriage is driven in a downward direction along the inclined thrust frame. As the drive carriage is driven downwardly, the pipe-rotation mechanism rotates the pipe about the boring axis, thereby causing the pipe (with boring tool mounted thereon) to drill or bore a hole.
As the drilling operation proceeds, the drill string is lengthened by adding pipe sections to the string. Typically, the pipe sections are provided with a male threaded connector on one end and a female threaded connector on the other end. Each time a pipe section is added to the drill string, the pipe section being added is aligned with the drill string and the threaded connector on its distal end is mated with the threaded connector on the proximal end of the drill string. Obviously, either the pipe section being added or the drill string must be restrained against rotation while the other component is rotated to engage the threaded connector on the distal end of the pipe section with the threaded connector on the proximal end of the drill string to create a secure threaded connection between the components.
During drilling using a horizontal directional drill, drilling fluid can be pumped through the drill string, over the boring tool at the distal end of the drill string and back up through the hole, to remove cuttings and displaced dirt. After the boring tool reaches a desired depth, it can be directed along a generally horizontal path and back up to break the surface of the ground at a distant point. To control the direction of the borehole, a boring tool with an angled-face may be used. When the direction of the borehole must be changed, the drill bit is positioned with the angled-face oriented in the desired direction. The drill string is then pushed through the ground without rotation, and the angled-face of the boring tool causes the drill string to deflect in the desired direction. This ability to change the direction of travel of the drill string also allows the operator to steer the drill string around underground obstacles like large roots and rocks.
Sufficient lengths of pipe are added to the drill string as needed to reach the exit point where the boring tool emerges from the earth. When the original bore is complete, it may be enlarged by replacing the boring tool with an enlarging device, commonly known as a backreamer. The backreamer is connected to the distal end of the drill string and moved through the original bore back towards the boring machine, either with or without rotation of the drill string. The backreamer expands and stabilizes the walls of the bore, generally while pulling a utility line or other underground component through the enlarged bore behind it. Movement of the backreamer back towards the drilling machine is accomplished by driving the drive carriage in a rearward direction on the thrust frame to withdraw a pipe section, disconnecting the withdrawn pipe section from the drill string, connecting the next pipe section in the drill string to the pipe rotation mechanism on the drive carriage and repeating the process until all of the pipe sections have been withdrawn from the ground. As each pipe section in the drill string is uncoupled from the drill string, it is loaded back into the pipe section magazine of the directional drilling machine.
Directional drilling machines frequently include a plurality of hydraulic motors and hydraulic actuators. Generally these hydraulic systems require one or more hydraulic pumps and a hydraulic fluid storage tank of significant size. In conventional directional drilling machines, the hydraulic fluid tank is raised above the centerline of the pump suction port or ports in order to provide sufficient head for efficient operation. However, such constructions result in a high center of mass of the machine, which makes it somewhat unstable. In addition, such constructions place the hydraulic fluid tank adjacent to the pump or pumps and/or the driving engine, thereby enlarging the machine's profile or making it difficult to access the pumps and/or engine for service. It would be desirable if a hydraulic tank construction for a drilling machine could be provided that would overcome these disadvantages of conventional constructions.